The overall objective of this project is to increase our understanding of the interactions of ions (primarily Ca) with the sarcolemmal membrane (SL) of cardiac muscle. Emphasis is placed on the role of SL Ca transport in cardiac excitation-contraction coupling. These studies, using isolated SL vesicles, will include measurements of enzyme activities and ion binding and transport. Attempts will be made at each step to relate biochemical findings to data which has been obtained from intact cardiac tissue. We have been successful in the laboratory in developing a procedure for the isolation of highly purified (about 80-fold) cardiac sarcolemma. Using this SL we have developed techniques for the accurate measurement, of Ca binding, Na-Ca exchange, and Ca efflux. With these techniques we now plan to further study the basic properties of Ca-SL interactions. This will be accomplished through the use of separated inside and right-side vesicles, by study of the effect of various interventions on the Na-Ca exchange mechanism, and by comparison of Na-Ca exchange properties in different species and tissues. The effects of ischemia and various drugs on various measures of SL integrity will also be ascertained. The interaction of ions with the SL is of central importance in understanding both normal and abnormal cardiac function. The different aspects of the proposed research all focus on this problem.